External appearance is important to practically everybody. In recent years, methods and apparatuses have been developed for different cosmetic treatments to improve external appearance. Among these are: hair removal, treatment of vascular lesions, wrinkle reduction, collagen destruction, circumference reduction, skin rejuvenation, and others. In these treatments, a volume of skin to be treated is heated to a temperature that is sufficiently high as to perform the treatment and produce one of the desired treatment effects. The treatment temperature is typically in the range of 38-60 degrees Celsius.
One method used for heating the epidermal and dermal layers of the skin is pulsed or continuous radio frequency (RF) energy. In this method, electrodes are applied to the skin and an RF voltage, in a continuous or pulse mode, is applied across the electrodes. The properties of the voltage are selected to generate an RF induced current in the skin to be treated. The current heats the skin to the required temperature and causes a desired effect, performing one or more of the listed above treatments.
Another method used for heating the epidermal and dermal layers of the skin is illuminating the skin segment to be treated by optical, typically infrared (IR) radiation. In this method, a segment of skin is illuminated by optical radiation in a continuous or pulse mode. The power of the radiation is set to produce a desired skin effect. The IR radiation heats the skin to the required temperature and causes one or more of the desired effects.
An additional method used for heating the epidermal and dermal layers of the skin is application of ultrasound energy to the skin. In this method, ultrasound transducers are coupled to the skin and ultrasound energy is applied to the skin between the transducers. The properties of the ultrasound energy are selected to heat a target volume of the skin (usually the volume between the electrodes) to a desired temperature, causing one or more of the desired treatment effects, which may be hair removal, collagen destruction, circumference reduction, skin rejuvenation, and others.
Methods exist which simultaneously apply a combination of one or more skin heating techniques to the skin. Because all of the methods alter the skin temperature, monitoring of the temperature is frequently used to control the treatment. In order to continuously monitor skin temperature, suitable sensors such as a thermocouple or a thermistor could be built into the electrodes or transducers through which the energy is applied to the skin. Despite the temperature monitoring, certain potential skin damage risks still exist, since the sensor response time depends on heat conductivity from the skin to the sensor and inside the sensor, and may be too long and even damaging to the skin before the sensor reduces or cuts off the skin heating power. To some extent, this risk can be avoided by reducing the cut-off temperature limit operating the sources of optical radiation, RF energy, and ultrasound energy. However, this would limit the RF energy transmitted to the skin and the treatment efficacy. In some instances, for example, when the applicator is static, the temperature of the skin (and of the electrodes) may increase fast enough to cause skin damage.
The devices delivering energy to the skin, such as electrodes, transducers and similar are usually packed in a convenient casing, an applicator, operative to be held and moved across the skin. The user has to adjust applicator movement speed to a given constant skin heating energy supply, such as to enable optimal or proper skin treatment. However, at present the user has no indication if the selected applicator speed is proper or not.
There is a need to provide a method to alert or signify the user as early as possible of the undesired skin or electrode temperature changes. There is also a need to allow the user to adapt applicator movement speed at constant skin heating energy supply, enabling optimal or proper skin treatment. This is especially important for the fast developing field of personal skin treatment apparatuses enabling their safe use, as the typical user of such apparatus may be inexperienced.